1. Field of the Invention
The present invention relates to a refrigerant cycle having a gas refrigerant bypass passage through which gas refrigerant discharged from a compressor is introduced into an evaporator after being decompressed, while bypassing a condenser. More particularly, the present invention relates to a refrigerant cycle for a vehicle air conditioner, in which refrigerant amount circulating in the refrigerant cycle is suitably controlled according to super-heating degree (SH) of refrigerant discharged from the compressor.
2. Description of Related Art
In a conventional vehicle air conditioner, hot water (engine-cooling water) circulates in a heating heat exchanger during a heating mode, and air blown into a passenger compartment is heated by the heating heat exchanger. When temperature of hot water is low, air blown into the passenger compartment is not sufficiently heated by the heating heat exchanger.
To overcome the problem, a refrigerant cycle having a gas refrigerant bypass passage is described in JP-A-5-272817. In the conventional refrigerant cycle, when temperature of hot water flowing into the heating heat exchanger is lower than a predetermined temperature, gas refrigerant discharged from the compressor is directly introduced into an evaporator while bypassing a condenser, so that air passing through the evaporator is heated by gas refrigerant introduced into the evaporator. Further, a pressure of refrigerant discharged from the compressor or a super-heating degree of refrigerant at an outlet of the evaporator is detected, and it is determined whether refrigerant amount circulating in the refrigerant cycle is excess or deficient. However, the pressure of refrigerant discharged from the compressor is changed in accordance with refrigerant-cycle condition such as heat load of the refrigerant cycle, a rotation speed of the compressor, a decompressed degree of a decompression unit disposed in the gas refrigerant bypass passage. Therefore, it is difficult to accurately control the refrigerant amount by only the pressure of refrigerant discharged from the compressor.